1. Field of the Invention
The present invention relates to an upconversion laser that, with an infrared semiconductor laser of high output or an external resonance laser as a pump light source, by making use of upconversion phenomena of a rare earth doped optical fiber, outputs visible light for display use.
2. Description of the Related Art
First, an explanation of conventional upconversion due to a rare earth doped optical fiber will be given in the following.
As to upconversion to blue light, there is a report in which infrared light excites tri-valent thulium ions (Tm3+) to let oscillate with a wavelength of around 480 nm. According to Japanese Patent Laid-open Publication (KOKAI) No. HEI 8-307000 titled xe2x80x9cRare earth ion doped short wavelength laser apparatus, rare earth ion doped short wavelength light amplifier and rare earth ion doped wavelength converterxe2x80x9d, an upconversion is proposed in which wavelengths of approximately 1200 nm and approximately 650 nm are up-converted to an wavelength of approximately 480 nm. Though it says that efficient upconversion can be realized due to excitation with two wavelengths, a blue wavelength of 480 nm is a little longer for as the blue light for display use, being inappropriate for display use.
Similarly, Japanese Patent Laid-open Publication (KOKAI) No. HEI 7-142806 titled xe2x80x9cRare earth ion doped short wavelength laser light sourcexe2x80x9d and Japanese Patent Laid-open Publication No. (KOKAI) HEI 9-107143 titled xe2x80x9cBlue up-conversion laserxe2x80x9d disclose the following invention. That is, by means of an infrared laser of one wavelength (800 to 980 nm, for instance 850 nm), an optical fiber doped by trivalent praseodymium ion (Pr3+) and trivalent ytterbium ion (Yb3+) can be excited. By use of laser oscillation of Yb3+ ion of approximately 1020 nm followed the above excitation, Pr3+ ion is excited to obtain blue emission of 490 nm.
Thus, it has been proposed to upconvert infrared light to blue light, however, there has not yet been disclosed to upconvert to the blue of a wavelength of approximately 470 nm appropriate for display.
In Japanese Patent Application No. HEI 11-149751 titled xe2x80x9cUp-conversion Fiber Laserxe2x80x9d, which the present inventors have proposed, an up-conversion fiber laser is disclosed to obtain blue light appropriate for display. This application, with a red emitting superluminescent diode (SLD) as a pump light source, up-converts to two wavelengths of 450 nm and 480 nm, followed by mixing thereof to obtain blue color for display.
Though it might be improved in the future, there is a disadvantage that, at the present time, despite SLD""s for infrared wavelength having been already mass-produced to be relatively inexpensive, SLD""s for red wavelength are rather expensive from the viewpoint of cost. In addition to this, there is also another demerit that products of high output power are difficult to procure.
As a method that outputs red laser light, there is one that up-convert from infrared wavelength. A Pr3+ ion doped fiber is practically used in a Pr3+ ion doped optical fiber amplifier (PDFA) in which with infrared wavelength as a pump light source, signal of a band of 1.3 xcexcm is amplified. Other than this, it is known that due to the upconversion, blue, green and red emissions can be generated.
In xe2x80x9cHigh-power continuous-wave upconversion fiber laser at room temperaturexe2x80x9d, Optics letter/vol.22, No.11/June 1, 1997, by T. Sandrock et al, they say that from a Pr3+ and Yb3+ ion doped fiber, with exciting light of approximately 850 nm, 635 nm laser light of high output power can be obtained.
Further, similarly, also U.S. Pat. No. 5,805,631 xe2x80x9cBlue, Green, Orange, and Red Upconversion Laserxe2x80x9d proposes to obtain blue, green, orange and red colors from a Pr3+ and Yb3+ ion doped fiber.
In employing the Pr3+ and Yb3+ ion doped fiber, pump light of one wavelength is said to be capable of exciting. However, from the viewpoint of efficiency, a wavelength appropriate for ground state absorption (GSA) of Yb3+ and a wavelength appropriate for excited state absorption (ESA) are not the same. Accordingly, excitation with one wavelength constitutes a state of poor efficiency. When assumed realization of high power laser, this point causes problems.
Now, there are two bands of 630 nm and 680 nm in a red emission line spectrum of Pr3+ ion. According to xe2x80x9cDirect observation of time-resolved excited state absorption on Tm3+-doped various glasses using a laser-flash pump-probe spectroscopyxe2x80x9d, J. Non-Cryst. Solids, 1997 by S. Kishimoto et al, these wavelengths are known to be ones appropriate for ground state absorption (GSA) and excited state absorption (ESA) of Tm3+ ion.
However, so far, in the case of employing Pr3+ ion, the up-converted laser light is the final output and is not employed again as exciting light. Accordingly, precious properties of Pr3+ ion of having wavelengths appropriate for excitation of Tm3+ ion is not made the best use of.
An object of the present invention is to provide an upconversion laser in which a semiconductor laser of high output power can be used as a pump light source and wavelengths of the up-converted laser light are ones appropriate for display.
Another object of the present invention is to provide an upconversion laser capable of being excited with more efficient wavelengths.
To achieve the above ends, the present invention comprises a first upconversion laser performing upconversion excitation of praseodymium ion (Pr3+), and a second upconversion laser exciting thulium ion (Tm3+) by laser light of wavelengths of approximately 635 nm and approximately 685 nm that are obtained from the first upconversion laser. Here, the output laser light of the second upconversion laser has wavelengths of approximately 450 nm and/or approximately 480 nm.
Thereby, the wavelengths emitted from Pr3+ ion being ones just appropriate for excitation of Tm3+ ion, conversion from red laser light to blue laser light can be performed with high efficiency. Thereby, as the pump light source, external resonance type LD, SLD and LD that have high output power in infrared wavelengths can be used, resulting in blue laser light optimum for display.
The present invention comprises a first cavity and a second cavity. The first cavity comprises an external resonance type laser and a praseodymium ion (Pr3+) doped fiber, wherein with laser light emitted from the external resonance type laser as exciting light, the praseodymium ion is excited by upconversion to emit red light, the red light being resonated to oscillate laser. The second cavity comprises a thulium ion (Tm3+) doped optical fiber, wherein with the red light as exciting light, the thulium ion is excited by upconversion to generate blue light, the blue light being resonated to oscillate laser.
Thereby, as the pump light source, external resonance infrared LD of high output power can be selected, resulting in use of the selected device of high output power. Even if high output power is required in displaying a large image screen, blue laser light most appropriate for display can be obtained.
Furthermore, the present invention comprises a cavity, a Pr3+ and Yb3+ ion doped optical fiber, and a resonator structure. The cavity includes an external resonance laser that emits two kinds of laser lights of wavelengths of 780 nm to 900 nm and 950 nm to 1050 nm. The Pr3+ and Yb3+ ion doped optical fiber is disposed in the cavity and the laser light is inputted thereon. The resonant structure is disposed in the cavity, and causes the red light emitted through upconversion by the optical fiber to resonate.
Thereby, the up-converted red laser light can be obtained with a high efficiency.
Still further, the present invention comprises a cavity, a Pr3+ and Yb3+ ion doped optical fiber, and a resonant structure. The cavity includes an external resonance laser that emits two kinds of laser lights of wavelengths at 780 nm to 900 nm and 950 nm to 1050 nm. The Pr3+ and Yb3+ ions doped optical fiber is disposed in the cavity and the laser light is inputted thereon. The resonant structure is disposed in the cavity, and causes the green light generated through upconversion by the optical fiber to resonate.
Thereby, the up-converted green laser light of high efficiency can be obtained.